Method of blasting under high pressure conditions at elevated and normal temperatures

ABSTRACT

A METHOD OF BLASTING IN DEEP WELLS, WHERE EXPLOSIVE COMPOSITIONS ARE SUBJECT TO HIGH AMBIENT PRESSURES AND TEMPERATURES RANGING FROM NORMAL TO AS HIGH AS 300* F., INCLUDES PREPARING A FLUID EXPLOSIVE COMPOSITION COMPRISING A BLEND OF POLYNITRATED AROMATIC HYDROCARBON OF NORMALLY SOLID HIGH EXPLOSIVE TYPE SUCH AS TRINITROTOLUENE AT LEAST PARTIALLY DISSOLVED IN A LIQUID NITRATED AROMATIC HYDROCARBON SUCH AS NITROBENZENE, MONONITROTOLUENE AND DINITROTOLUENE AND MIXTURE OF THESE. THE COMPOSITION IS PRREPARED AT A TEMPERATURE HIGH ENOUGH TO RENDER IT PUMPABLE DUE TO SUFFICIENT DISSOLUTION OF THE HIGH EXPLOSIVE POLYNITRATE HYDROCARBON IN THE LIQUID HYDROCARBON. WHILE THE COMPOSITION REMAINS FLUID, IT IS PUMPED INTO THE DEEP WELL OR BOREHOLE.

United States Patent Office 3,811,971 Patented May 21., 1974 3,811,971 METHOD OF BLASTING UNDER HIGH PRESSURE CONDITIONS AT ELEVATED AND NORMAL TEMPERATURES Melvin Alonzo Cook, Albert G. Funk, and Gary L. Hansen, Salt Lake City, Utah, assignors to Ireco Chemicals No Drawing. Continuation of abandoned application Ser. No. 157,660, June 28, 1971. This application July 5, 1973, Ser. No. 376,286

Int. Cl. C06b /02 US. Cl. 149-92 7 Claims ABSTRACT OF THE DISCLOSURE A method of blasting in deep wells, Where explosive compositions are subject to high ambient pressures and temperatures ranging from normal to as high as 300 F., includes preparing a fluid explosive composition comprising a blend of polynitrated aromatic hydrocarbon of normally solid high explosive type such as trinitrotoluene at least partially dissolved in a liquid nitrated aromatic hydrocarbon such as nitrobenzene, mononitrotoluene and dinitrotoluene and mixture of these. The composition is prepared at a temperature high enough to render it pumpable due to sufficient dissolution of the high explosive polynitrated hydrocarbon in the liquid hy-- drocarbon. While the composition remains fluid, it is pumped into the deep well or borehole.

This is a continuation of application Ser. No. 157,660, filed June 28, 1971, now abandoned.

BACKGROUND AND PRIOR ART It is sometimes desirable or necessary to produce a powerful explosion at great depth below the surface of the earth. For example, it may become necessary to crush or break-in the formation around a gas or oil well, in order to cut off or restrict runaway flow, e.g., in case of unmanageable gas or oil well fires.

Explosive charges have been long used for completing" or increasing the production of wells drilled to recover earth fluids, such as water, oil and natural gas. Such charges may be used for springing the hole, i.e., enlarging it at the depth where the producing formation is found, or for fracturing the formations to produce fissures in rock, such fissures extending from the borehole radially into the formation to facilitate fluid fiow into the well. Such fissures are sometimes produced mechanically, as by application of hydraulic pressure, to fracture the producing formation only. Explosive charges have long been used for this purpose. Such charges commonly confined to the depth or area to be fractured by plugging the well with sand, concrete, etc., above and/or below the producing formation. Liquid nitroglycerin, despite hazards inherent in its use, has been used as the explosive composition; in later years blasting gelatins, high ammonium nitrate compositions and other compositions have been employed for the purpose.

Slurry compositions containing ammonium nitrate as a major ingredient and having an aqueous continuous liquid phase are good blasting agents, but they often have a serious deficiency in that they may become insensitive and difiicult to detonate when placed in a pressured environment. In very deep walls containing a liquid, the ambient pressures can be as great as 10,000 p.s.i.g.; in many cases, pressures exceeding 5,000 p.s.i.g. are encountered. Moreover, in deep wels, temperatures are encountered which may be high enough in some cases to I ture of around 200 F. or more and the hydrostatic pressure at the bottom or toe of the well can be as much as 4,500 p.s.i.g. or more. A 15,000 foot well may have a bottom pressure of 7,000 p.s.i.g. or more, and a maximum temperature around 300 F. A few wells have been drilled to considerably greater depths than 15,000 feet. Conventional explosives are not suitable for use under such conditions. It is desirable to have an explosive available which can be detonated with certainty at high pressures, even up to 10,000 p.s.i.g., while remaining stable at least for a reasonable time, at temperatures as high as about 350 F.

It is desirable, also, to have an explosive in fluid or slurry form so that it can be pumped into place through a pipe or other suitable conduit. Pumpable compositions of many kinds are known, but most of them do not have the other required properties already discussed.

It is also desirable in some instances to pump a powerful explosive that is very insensitive when pumped but increases in sensitivity shortly thereafter. Thus where high temperatures may not be present an all-liquid explosive of TNT dissolved in a non-aqueous liquid such as nitrobenzene at 70 C., when pumped will be very insensitive but will increase in sensitivity upon cooling due to crystallization of part of the TNT. Finely divided aluminum may also be added.

Compositions made up of nitrobenzene, which is a liqupid, and amonium nitrate, are known, as well asother combinations of liquid and solid explosive ingredients, such as nitroglycerin and nitrocellulose, the socalled Sprengel explosives, those based on liquid oxygen and fuels, etc. Most of these are too hazardous or two unstable for purposes of the present invention.

The present invention is based on the discovery that certain non-aqueous slurries, containing an energetic liquid carrier such as nitrobenzene or analogous liquid nitro-aromatic, having some solvency for normally solid self-explosives such as TNT and related materials, and having particulate TNT or equivalent or analogous solid and stable high powered explosive suspended therein, are highly satisfactory for the exacting requirements of deep well shooting. These compositions have the characteristic advantages of aqueous slurries, or some of them, such as suitability for preparation in the field, pumpability for delivery to the point of use, and percent space efficiency due to their fluid nature. At the same time, they are high in energy, reliable under adverse conditions of use, and stable at elevated temperatures, even when confined for extended periods of time in the well. Where high temperatures are not present, an explosive comprising TNT dissolved in a non-aqueous liquid at a sufficiently high temperature to keep the TNT in solution may be pumped in an insensitive state which will become increasingly sensitive upon cooling and crystallization out of part of or all of the TNT.

SUMMARY OF THE INVENTION A non-aqueous slurry explosive composition is made up by dissolving in nitrobenzene or ortho-mononitrotoluene a suitable proportion of TNT, or Composition B, RDX or equivalent. Excess particulate TNT remains undissolved. Depending on the mixing temperature, from about 0.7 to 3.3 parts by weight of TNT can be dissolved in one part of liquid nitrobenzene. Typically to 40 or 50 parts of this liquid, 50 or 60 parts by weight of particulate TNT are added. A composition is produced which flows readily and is umpable. This mobile or liquid phase may also contain a suspension of very finely divided energetic fuel, such as finely divided aluminum. Flaked metallic aluminum of very fine grain size, preferably paint grade, is very satisfactory. The aluminum serves as a thickener and it makes the slurry smooth so that it does not separate and is easily pumped. Part or all of the nitrobenzene, NB, may be replaced with nitro-aromatic liquid, such as o-mononitrotoluene, o-MNT, or mixtures of dinitrotoluene, DNT, with o-MNT or NB. The solvents chosen, as well as the selfexplosive solute, TNT or equivalent, are chosen so as to make a compatible solution. Particulate self-explosive granules of the self-explosive are then suspended in the solution, which may also be thickened with a viscosity increasing or gelling agent, such as fumed alumino, Cabosil, etc. Where high temperatures may not be present, compositions may also be made, using only TNT dissolved in non-aqueous liquid, preferably nitrobenzene, at a sulficiently high temperature to keep the TNT in solution. This all-liquid explosive is very insensitive when hot but increases insensitivity upon cooling.

DESCRIPTION OF PREFERRED EMBODIMENT A composition was made for use in a deep oil Well by first preparing a solution of TNT in nitrobenzene. At 15 C. it was determined that about 0.7 parts by weight of pelleted TNT can be dissolved in one part of nitrobenzene. At higher temperatures solubility increases so that at 60 C. about three parts of TNT can be dissolved in one part of nitrobenzene. Solubility generally is between these limits, although somewhat smaller or larger proportions of TNT are soluble at more extreme temperatures. Orthomononitrotoluene has generally similar solubility for TNT and mixtures of o-MNT and dinitrotoluene are reasonably good solvents for TNT.

Example I A composition was made up of 22% by weight of nitrobenzene, 68% pelletized TNT (approximately 15 parts of which dissolved at room temperature) and paint grade or fine flaked aluminum coated with stearic acid. The order of mixing was not important. The fine aluminum acted as a thickener, making a smooth silvery liquid medium, which suspended the undissolved pellets of TNT and which could be pumped through a one-inch pipe without heavy back pressure. This product was not detonable with a No. 8 standard electric blasting cap.

The materials just described are readily pumpable at normal temperatures, ca. C. As such they can be pumped into the bottom of a well under pressures up to 10,000 p.s.i.g.

A number of tests were made to determine stability and detonability under simulated deep well conditions. Materials such as in Example I were confined in a 4-inch diameter steel pipe at 10,000 p.s.i.g. and 300 F. Attempts to initiate detonation through the pipe wall failed. It was found to be necessary to place a detonator in direct contact with the slurry to obtain a high order detonation. After 75 minutes storage at 10,000 p.s.i.g. and 300 F., a detonation was produced with a high velocity of 5820 m./sec.

Another sample of this slurry was tested for detonation after storage for 52 hours at 300 F. and pressure of 10,000 p.s.i.g. This composition also detonated with a velocity of 5820 m./sec.

Later, two additional samples of Example I were stored under pressure of 10,000 p.s.i.g. and at 300 F. for 48 and 72 hours, respectively. These were boostered by including numerous l-inch diameter charges of pressed RDX totaling 400 grams, 2 inches long, wrapped in aluminum foil with the slurry inside 4-inch pipes. These boosters remained in the bottoms of the pipes or test chambers during storage. They were initiated with a shaped charge from outside the pipe. Both charges fired at velocity above 5800 meters per second.

Example II A liquid explosive was made up by dissolving 75 parts by weight of TNT in 25 parts of nitrobenzene at 70 C. At this temperature nitrobenzene will dissolve TNT in a 3 to 1 parts by weight ratio of TNT/nitrobenzene. This liquid explosive at 70 C. failed to detonate with a 3 lb.

composition B booster. Thus the explosive at this temperature is very insensitive. However, as this explosive cooled it became much more sensitive, due to the crystallizing out of part of the TNT and the resultant suspension of fine TNT crystals in the solution. Table I shows the relative sensitivity of this explosive at 70 C. and 20 C.

TABLE I 25/75 Nitrobenzene/TNT At 70 C.

3" diameter pipe filled with the slurry charge detonated with gm. booster. 2 /2 diameter pipe charge fails with 160 gm.

booster. At 20 C.

1%" diameter pipe charge detonated with 160 gm.

booster. 1" diameter pipe charge fails with 160 gm. booster.

Thus the data in Table I shows that the sensitivity increases significantly when the temperature of the explosive is decreased from 70 C. to 20 C. As the temperature is lowered TNT crystallizes out of solution thereby increasing the sensitivity of the explosive.

By proper choice and proportioning of ingredients, highly efiicient explosives can be prepared. The judicious use of high energy fuels such as finely flaked aluminum gives considerable flexibility. Aluminum in fine flaked form is a powerful sensitizer in the presence of good oxidizers. However, if water is present in the borehole, then aluminum cannot be used. The optimum proportions of ingredients such as nitrobenzene, TNT, aluminum, etc., can readily be calculated and a reasonable approach can be realized while providing other desired properties such as fluidity, and low total cost of ingredients.

While TNT is commonly preferred as the particulate suspended high explosive solid ingredient, and nitrobenzene in which TNT has been dissolved is the preferred suspending fluid, other and related high explosives may be used. Thus, all or part of the particulate TNT may be replaced at least in part by RDX which is cyclotrimethylene trinitramine; Composition B, which is a mixture of TNT and RDX, can be used, at least in place of part of the TNT. Also, part of the TNT can be replaced by dinitrotoluene. The compounds, TNT, and DNT, are normally more soluble in nitrobenzene than RDX or HMX and are preferred as solutes in the liquid phase for this reason. However, the non-aromatic high exposives, such as RDX and HMX are satisfactory as particles to be suspended in the fluid medium.

Proportions of other ingredients may be varied, as already indicated to adjust the oxygen balance within limits which are compatible with the other properties named. Thus, proportions of 0.1 to as much as 20 weight percent of finely divided aluminum may be added. However, excessive amounts of aluminum may segregate; proportions of 5 to 15% are preferred. Other high energy metals, such as boron, magnesium, or silicon can be substituted for all or part of the aluminum; it should be noted, however, that magnesium particularly is more reactive than aluminum and less stable at high temperatures.

The use of thickeners, other than or additional to the dissolved TNT, etc., has been suggested above. Fumed alumina and Cabosil have been used to thicken the mix without any difliculty.

In general, the invention contemplates use of an organic non-aqueous solvent for nitrated organic self-explosive, such as TNT or equivalent, which is thick enough to serve as a suspending vehicle for solid particulate selfexplosive, which also is TNT or equivalent. By equivalent here is meant self-explosive nitrated organic compounds of high energy, high brisance, and stable enough to withstand decomposition or preignition, at least for a reasonable time, at temperatures as high as 300 F. TNT

and related aromatic compounds are preferred but nonaromatics can be used if sufficiently stable and if soluble, at least to a modest degree, in the solvent. As indicated above, nitrobenzene is the preferred solvent; mononitrotoluene or mixtures thereof with dinitrotoluene can be used in lieu of or at least to replace part of the nitrobenzene.

Of the preferred main ingredients, which are NB, TNT and aluminum, proportions of 15 to 60% by weight of nitrobenzene, 85 to 40% of TNT and to 20% aluminum can be used. A preferable range is 18 to 30% of nitrobenzene, 77 to 55% of TNT (including, of course, that which is dissolved in the nitrobenzene) and to 15% of aluminum. A more specific and particularly desirable range is 20 to 25% nitrobenzene, 60 to 70% TNT and 5 to 15 aluminum. Other fuels, such as powdered gilsonite, coal and other carbonaceous, carbohydrate or hydrocarbon type materials stable up to about 300 F. can be added if desired. For the explosive to be used at low temperatures it is possible to dissolve substantially all of the TNT in the non-aqueous liquid at a sufficiently high temperature for the TNT to remain in solution in order for the explosive to remain relatively insensitive at the mixing temperature.

Various other modifications and substitutions of ingredients, proportions, etc., may be used, as will be obvious to those skilled in the art.

What is claimed is:

1. A method of blasting in a deep well under high ambient pressure and having a temperature as high as 300 F. which includes the steps of preparing a fluid explosive composition comprising of a blend of polynitrated aromatic hydrocarbon of normally solid high explosive type at least partially dissolved in a liquid nitrated aromatic hydrocarbon selected from the group which consists of nitrobenzene, mononitrotoluene, dinitrotoluene, and mixtures of any two or more thereof at a temperature high enough to render the composition pumpable due to sufficient dissolution of the solid high explosive type bydrocarbon in the liquid hydrocarbon, and, pumping the explosive into the well.

2. A method according to claim 1 in which the composition contains up to 20% by weight of finely divided aluminum particles.

3. A method according to claim 1 in which the liquid nitrated aromatic hydrocarbon comprises 20 to by weight of the fiuid explosive composition.

4. A method according to claim 1 in which the polynitrated aromatic hydrocarbons of normally solid high explosive type are trinitrotoluene, cyclotrimethylenetrinitramine, hexamethylenetetramine, mixtures of these, and the like.

5. A method according to claim 1 wherein the explosive composition comprises 15 to by weight of nitrobenzene, 40 to of trinitrotoluene and up to 20% of finely divided aluminum particles.

6. A method of blasting in a deep well under high ambient pressure and having a temperature as high as 300 F. which includes the steps of preparing a fluid explosive composition comprised of 75 to by weight trinitrotoluene, dissolved in 5 to 25% liquid nitrated aromatic hydrocarbon selected from the group which consists of nitrobenzene, mononitrotoluene, dinitrotoluene, and mixtures of any two or more thereof at a temperature high enough so that substantially all of the trinitrotoluene remains in solution and pumping the explosive composition into the well before a substantial amount of trinitrotoluene crystallizes out of solution.

7. A method according to claim 6 wherein the explosive composition contains up to 20% of finely divided aluminum particles with correspondingly decreased amounts of trinitrotoluene and liquid hydrocarbon.

References Cited UNITED STATES PATENTS 3,271,212 9/1966 Riedl et a1 149-106 X STEPHEN I. LECHERT, 111., Primary Examiner US. Cl. X.R. 

